1. Field of the Invention
This invention relates to a video signal magnifying and reducing processing method for interlaced images suitable for use in an electronic zoom or the like used for television cameras.
2. Description of the Prior Art
In a conventional processing for magnifying an interlaced image, for example, for a twice magnification, origins Co, Ce of an odd field and an even field for the magnifying processing are set independently of each other, as shown in FIG. 1, and the intervals d between respective scanning lines (lines) lo, le of the odd and even fields constituting the original image are respectively magnified by a factor of two, and the interlace relationship between lines Lo, Le of the odd and even fields is maintained even in a magnified image.
Incidentally, in the example of FIG. 1 and so on, in a manner different from ordinary methods, the lines of the odd field are designated odd numbers while the lines of the even field are designated even numbers such that the lines in a reproduced image have sequential numbers.
In the case of FIG. 1, a bi-linear method, for example, is applied to each of the odd and even fields, as indicated by hatching and broken lines, to interpolate the space between lines, whereby the intervals between lines of the respective fields in the magnified image (scanning line density) are made equal to the scanning line density of the original image.
In the bi-linear method, assuming that a sampling point is represented by xi, an interpolated position by xj, and an interpolating function by f(x), an interpolation calculation is performed as given by the following equation (1): EQU I(xj)=I(xi)f(xj-xi)+I(xi+1)f(xj-xi+1) . . . (1) ##EQU1##
Further, as shown in FIG. 2, when the origins Co, Ce of the odd and even fields for a magnifying processing are respectively set at a common position, the respective lines Lo, Le of the odd and even fields in a magnified image are mutually interlaced, whereby the interpolation is performed between respective lines to make the scanning line density of the magnified image equal to that of the original image.
On the other hand, in a processing for reducing an interlaced image, for example, by a factor of two, origins Co, Ce of an odd field and an even field for the reduction processing are respectively set at a common position as shown in FIG. 3, and the interval between respective lines lo of the odd field constituting an original image is reduced by a factor of two, while the interval between respective lines le of the even field is reduced by a factor of two after interpolation between lines, thereby maintaining the interlace relationship between lines ldo, lde of the odd and even fields even in a reduced image.
In this event every other line constituting the original image is dropped in the odd field, while each pair of two adjacent lines is interpolated in the even field, thereby making the scanning line density of each field constituting the reduced image equal to the scanning line density of the original image.
The above-mentioned interpolation between lines, however, implies problems such as a line flicker, a flicker of the vertical resolution in each field or the like, in addition to deterioration of the vertical resolution in a still image.
More specifically, when the origins Co, Ce of the odd and even fields for magnification are set independently of each other as shown in the foregoing FIG. 1, magnification has been clearly carried out in each field. Nevertheless, since the phase of the origins Co, Ce for magnification are deviated from each other, the reproduced image vertically pitches in every field, thereby causing a line flicker phenomenon.
Further, when the origins Co, Ce of the odd and even field for magnification are located at a coincident position as shown in FIG. 2, the line flicker phenomenon as mentioned above is improved. However, the odd and even fields respectively have a different interpolation coefficient for performing the interpolation between lines as shown in FIG. 2, that is, stated other way, the odd and even fields respectively present different local filter characteristics, so that the degree of degradation of the vertical resolution in a reproduced image is different at every field, which results in generating a flicker of the vertical resolution.
Incidentally, when the origins Co, Ce of the odd and even fields for magnification are set independently of each other as shown in the foregoing FIG. 1, the local filter characteristic is equal in the odd and even fields, so that the flicker of the vertical resolution will not be generated.
On the other hand, when the origins Co, Ce of the odd and even fields for reduction are set at a common position as shown in the foregoing FIG. 3, the the local filter characteristic is different in the odd and even fields, so that the flicker of the vertical resolution is likewise generated.